A battery for supplying power is required to operate various types of portable devices including a portable phone and a charging type battery is widely used as the battery. Wired (contact) charging is typically applied to the charging type battery, but in recent years, contactless (wireless) charging has been widely used.
One of the most generally contactless charging types is an electromagnetic induction type and FIG. 7 is a conceptual diagram of a general electromagnetic induction type contactless charging system. As illustrated in the drawing, the contactless charging system 100 includes a transmitter 110 and a receiver 120. The transmitter 110 includes a transmission circuit 112 that operates by receiving AC power 111 and a primary coil 113 for electromagnetic induction. The receiver 120 includes a secondary coil 121 that causes the electromagnetic induction with the primary coil 113 of the transmitter 110 and a charging circuit 122. When a battery 130 is connected to the charging circuit 122 of the receiver 120 and the secondary coil 121 is positioned at a predetermined location of the primary coil 113 that receives the AC power, the battery 130 is charged by the electromagnetic induction.
Electromagnetic induction type contactless charging for the portable device represented as the portable phone is standardized in the Wireless Power Consortium (WPC). The WPC uses a charging frequency (i.e., 110 to 205 kHz) in a predetermined band in power transmission by the electromagnetic induction and standardizes the electromagnetic induction type contactless charging for charging within a transmission distance of tens of millimeters.
The contactless charging system applied to the portable phone includes a type that uses a ‘charging cover’ independent from the portable phone. The receiver including the secondary coil and the charging circuit is installed in the charging cover. While a battery of the portable phone is electrically connected to the charging cover by a connector or a cable, the charging cover is loaded on the transmitter (charging pad) to charge the battery. However, when the charging cover is used, there is inconvenience that the charging cover needs to be additionally provided for the contactless charging of the portable phone.
Instead of the charging cover, there has been developed a product in which the receiver (including the secondary coil and the charging circuit, in this case, the charging circuit may be installed in a body of the portable phone) is installed in a battery cover (a rear cover a plastic synthetic resin injection matter which opens and closes a rear surface of the portable phone in order to replace the battery) which is a part of the portable phone to execute the contactless charging by the portable phone itself without the additionally charging cover.
FIG. 8 is a schematic cross-sectional view of a known contactless charging system applied to the portable phone. The contactless charging system 200 of FIG. 8 includes a charging pad 210 which is the transmitter and a battery cover 220 of the portable phone which is the receiver.
The charging pad (transmitter) 210 is embedded with components of the transmitter in a case 211 made of a plastic synthetic resin. In detail, the charging pad 210 has a structure in which a circuit substrate 212 is laminated on a bottom of the case 211, ferrite 213 is laminated thereon and thereafter, a loop-shaped primary coil 214 is laminated on the ferrite 213 and a permanent magnet 215 is installed at the center of the primary coil 214. The battery cover (receiver) 220 has a structure in which ferrite 222 and a secondary coil 223 are buried in a plastic injection matter 221, however, the ferrite 222 is laminated between the battery cover 220 and the battery 230 in an upper part of the battery cover 220, and the secondary coil 223 is laminated on a bottom of the ferrite 222.
In the contactless charging by the electromagnetic induction, when the secondary coil is position at a predetermined location of the primary coil (when a center point of the primary coil and a center point of the secondary coil vertically coincide with each other), maximum charging efficiency is achieved. In this case, as the secondary coil deviates from a regular position with respect to the primary coil, charging efficiency is decreased due to transfer loss of a magnetic field and heat is emitted while compensating the decreased charging efficiency. Further, when the secondary coil is further distant from the primary coil by a predetermined deviation distance (i.e., 20 mm) or more, an electromagnetic field formed in the primary coil cannot be sufficiently transferred to the secondary coil, and as a result, charging is stopped.
The aforementioned Wireless Power Consortium (WPC) presents several standards as a measure for increasing the charging efficiency of the contactless charging.
A first standard is a “magnet type contactless charging system” that the permanent magnet is installed at the centers (alternatively, only at the center of the primary coil) of the primary coil and the secondary coil to induce a position of a quantum coil to the regular position by magnetic force.
A second standard is a “coil movable contactless charging system” that regularly positions the secondary coil to the primary coil by moving the primary coil to the position of the secondary coil with a stepping motor by detecting the position of the secondary coil when the receiver (secondary coil) is loaded on the transmitter (primary coil).
A third standard is a “plural coil type contactless charging system” that when a plurality of primary coils are installed and the secondary coil is loaded thereon, current is applied to the primary coil which is most adjacent to the secondary coil to increase induced electromotive force between the primary coil and the secondary coil.
The “coil movable contactless charging system” and the “plural coil type contactless charging system” have a problem that a product price is relatively increased due to an increase of the number of components as compared with the “magnet type contactless charging system”. In particular, the “coil movable contactless charging system” has a limit in restricting a weight of the primary coil in order to reduce a load applied to the stepping motor. The “plurality coil type contactless charging system” has a problem that the size of the transmitter is excessively increased due to an array structure of the primary coils, while the sizes of the primary coils need to be restricted.
By such a background, in the “coil movable contactless charging system” and the “plural coil type contactless charging system”, the charging efficiency is decreased by 10% or more as compared with the “magnet type contactless charging system”, and as a result, practically, the “magnet type contactless charging system” is used relatively more.
However, the “magnet type contactless charging system” has a problem that although the position of the quantum coil may be maintained to the regular position at relatively low cost, when this is applied to the portable phone, the size and the weight of the portable phone are increased due to addition of the magnet and the applied magnet may cause a misoperation of a magnetic field using device (i.e., a compass, a gyro sensor, and the like) embedded in the portable phone.
The contactless charging system 200 of FIG. 8 applied to the portable phone has a configuration in which a permanent magnet 215 is installed only in the charging pad 210 and the ferrite 222 of the battery cover 220 is thus attached to the permanent magnet 215 to induce the position of the secondary coil to the regular position of the primary coil. When the permanent magnet 215 is to be applied to only the primary coil 214 as described above, magnetic force of the permanent magnet acts on the ferrite 222 having a large area, and as a result, since a deviation of the position of the secondary coil from the position of the primary coil may occur, it is difficult to ensure optimal charging efficiency. Further, in order to prevent the electromagnetic field from being distorted due to interaction of a permanent magnet having a high intensity of the magnetic field and high permeability and a metallic element of the battery, relatively thick ferrite 222 needs to be used for the battery cover 220, which exerts a bad influence on minimization and weight lightening of the portable phone.
The WPC standard presents a “variable frequency type contactless charging system” as another method that supplements the charging efficiency of the electromagnetic induction type contactless charging system.
A “variable frequency type” is a scheme that by applying an algorithm of a proportional integral differential (PID) control for a best power transmission control, the charging frequency used in the contactless charging is varied in proportion to the charging efficiency and the power of the transmitting unit is varied in inverse proportion to the charging efficiency (see 5.2.3.1 Power transfer control of WPC Spec Ver 1.0.3).
The “variable frequency type” is independently applied or together applied in merge with the aforementioned “magnet type contactless charging system” or “coil movable contactless charging system”.
The “variable frequency type” uses the charging frequency used in the contactless charging variably in proportion to the charging efficiency, for example, in the range of minimum 110 kHz and maximum 205 kHz. For example, as the primary coil and the secondary coil get close to the regular position (as the charging efficiency is higher), a charging frequency which gets close to 205 kHz is used and as the second coil is further separated from the regular position relative to the primary coil (as the charging efficiency is lower), current applied to the primary coil is increased while using a charging frequency which gets close to 110 kHz to maintain the charging efficiency of the battery at least at predetermined charging efficiency or more.
That is, in the “variable frequency type”, when as the primary coil of the transmitting unit and the secondary coil of the receiving unit get close to the regular position, relatively more electromagnetic fields are transferred, and as a result, when the power transfer loss is relatively lower, the transmitting unit applies relative lower power having a relatively higher charging frequency, whereas when as the quantum coil is further separated from the regular position, a relatively lower electric field is transferred and the power transfer loss is relatively high, high power having a relatively lower charging frequency is applied to the primary coil to supplement charging efficiency loss by separation of the secondary coil from the regular position relative to the primary coil.
However, in the “variable frequency type”, although the charging efficiency is supplemented by changing the charging frequency and the power, for example, when the secondary coil is positioned at an outermost position within a primary coil chargeable range, the charging efficiency is decreased as compared with maximum charging efficiency by approximately 20% or more and in this case, serious heat emission is caused due to an excessive increase of power applied for supplementing the charging efficiency.
In the known contactless charging system described above, the secondary coil deviates from the regular position relative to the primary coil, but when the secondary coil is within a chargeable range, charging is executed and it is marked that the secondary coil is in charge, and as a result, a user cannot know a state that the charging efficiency is low and heat is emitted and continuously performs charging. Consequently, unnecessary power consumption may be caused or a safety problem may occur due to the heat emission.
Accordingly, in the electromagnetic induction type contactless charging system, it is very important to position the secondary coil from the regular position of the primary coil and the heat emission needs to be minimized even though the secondary coil deviates from the regular position of the primary coil.
Related art associated with the contactless charging of the portable phone includes ‘Contactless Charging System of Wireless Phone’ of Korean Patent Application Issue No. 10-1995-0005819 (Issued on May 31, 1995) and ‘Wireless Charging Device’ of Korean Utility Model No. 20-0217303 (registered on Jan. 8, 2001).
In association with enhancement of the charging efficiency in the electromagnetic induction type contactless charging, there are proposed methods that induce the user to perform charging at higher charging efficiency by detecting (current or voltage) and acquiring the charging efficiency based on the detected power to be displayed to the user.
In percentage efficiency acquired by detecting the power (current or voltage) in the portable phone, a ratio of power consumed in an output for power supplied from an input may be represented by a percentage, that is, (Power_out/Power_in)×100. Herein, “Power_out” represents “charging voltage×charging current” of the battery and is controlled in the portable phone and “Power_In” represents “supply voltage×consumed current” of the transmitting unit (charging pad).
For example, when it is assumed that charging voltage supplied to the battery is 5 V in a rectifier circuit (Power_out) of the secondary coil and charging current is charged with 600 mA, the output power (Power_out) is 3 W and charging efficiency of power consumed in the primary coil of the charging pad is approximately 70% when it is assumed that DC supply voltage (i.e., 19 V) of the charging pad is constant and consumed current of the charging pad is approximately 226 mA.
The percentage charging efficiency acquired by detecting the power (voltage or current) may be acquired only by measuring both input power of the charging pad and output (charging) power of the portable phone and thereafter, transferring a value measured in one device (the charging pad which is the transmitting unit or the portable phone which is the receiving unit) to the other device (the portable phone which is the receiving unit or the charging pad which is the transmitting unit).
However, since two devices (the charging pad and the portable phone) are separated from each other, an additional wireless communication means for data transmission is required to transfer the power (current or voltage) measured in any one device to the other device, and as a result, calculation of the charging efficiency by the measurement value of the power (voltage or current) is an inefficient and very complicated method.
Moreover, in, for example, a lithium ion (Li-ion) or lithium polymer (Li-Polymer) battery, in order to ensure stability such as preventing the danger of explosion by rapid charging and discharging, when it is considered that charging current introduced into the battery is appropriately controlled in the portable phone (i.e., Trickle Charge, Pre-Charge, Fast Charge, and End of charge) and the charging voltage is also requested to be constantly maintained, calculation of the charging efficiency based on the power (voltage or current) is not easily applied to an actual use environment of the portable phone.
Other related art for enhancing the charging efficiency of the contactless charging system includes ‘System and Method of Wireless Charging’ of Korean Patent Application Laid-Open No. 10-2010-0074595 (published on Jul. 2, 2010), ‘Contactless Charging Device’ of Korean Patent Registration No. 10-1063154 (registered on Sep. 1, 2011), ‘Position Recognition Contactless Power Supply Device and Battery Charging Device and Charging System Using the Same’ of Korean Patent Application Laid-Open No. 10-2009-0025876 (published on Mar. 11, 2009), and ‘Contactless Charging Device having Charging State Display Function and Charging Method Thereof’ of Korean Patent Application Laid-Open No. 10-2009-0059507 (Jun. 11, 2009).